Good post Car, generated a lot of opinion.
The speedy boarding option is a relatively expensive extra I feel, and there are no guartantees that you will get seats together. If you go for this as others have said, you need to get yourselves to the gate but beware, queues form early and you may find that many of those people are in boarding group B not speedy boarders and you could find you have lost your chance. Also as has been said earlier SB sometimes means you first on the bus (which probably means last on the plane!). However if you have young kids and for peace of mind you could go for it. It can be a bit of a bunfight though and you may need to be assertive, not always easy with young kids in tow.!
For older kids and adults, it is probably not so much a problem, in fact they may prefer a bit of independance. Personally I usually ask at checkin how many people are on the flight. The planes take about 156 I think, so you can get an idea how busy the flight is and your chances of getting seats together. If it is full get to the gate in good time and be prepared to queue.
If on the plane you are stuck, watch out for couples where one is in the aisle and the other at the window. Chance are they will not want you sitting in the middle and will

kindly offer to move !. At least you may get 2 aisle seats together.
I must say I prefer to have allocated seats but the low cost airlines don't seem to like this. I suspect it has the effect of getting everone on the plane quicker in the rush for seats.
Despite the above I would not be put off too much. Easyjet are much preferable to the other low cost airline run by Mr O' L in my opinion.
Adios
Dave